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| Home > Publications database > Ablagerung und Frühdiagenese organischen Materials in marinen Hochproduktivitätsgebieten |
| Book/Report | FZJ-2019-02120 |
1997
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21986
Report No.: Juel-3413
Abstract: This study incorporates a detailed interdisciplinary approach involving geochemistry and microscopy to characterise organic matter in upwelling sediments along the continental margins of Peru and Oman. The sediments were drilled during 'Ocean Drilling Program (ODP)'-Leg 112 (Sites 679, 681 and 688) and Leg 117 (Sites 720, 723 and 724), respectively. In addition sampIes from a high productivity area off Pakistan in the northem Arabian Sea were inc1uded to enable a comparison. The purpose of these investigations were to provide an insight into the origin of sedimentary organic matter in marine high productivity areas and subsequently to integrate these findings into sedimentation models and to demonstrate sedimentation processes. Over 250 samples from 14 different bore holes were investigated. The microscopic and organic/inorganic geochemical methods utilized were: Reflected light microscopy, transmitted light microscopy, transmission electron microscopy (TEM) , scanning electron microscopy (SEM), elemental analysis of organic carbon, sulfur, iron and nitrogen, Rock-Eval pyrolysis, pyrolysis-gas-chromatography and kinetic experiments of the hydrocarbon generation potential. The high content of organic carbon (up to 10 wt.-%) found in sediments deposited under an intense oxygen minimum zone suggested in the past that oxygen deficient environments are important for the preservation of organic matter. However, microscopic and nanoscopic investigations revealed that the structural integrity of primary organic matter is slight. Furthermore, it appears that in sediments under the immediate influence of high productivityareas, microbially catalyzed degradation processes within the water column result in the decay of primary organic material. The organic matter in sediments deposited undemeath such high productivity zones consist mainly (up to 99 vol.-%) of unstructured organic aggregates. In sediments outside these upwelling zones terrigenous organic particles are predominant. The primary marine organic matter has been almost completely remineralized. The fraction of organic matter reaching the sediment surface was calculated to be at the most 10 %, even if the bioproductivity in the photic layer of the water column is high. At most investigated locations, further oxidation reactions of organic matter in the sediment led to oxygen depletion, resulting in the establishment of an anoxie environment and the initiation of anaerobic degradation processes. This anoxic zone was found a few centimeters below the sediment/water-interface. The deposition of organic matter shows a broad spatial and temporal variability. The geochemical investigations suggest that the depositional conditions offshore Peru are less variable than those from the Arabian Sea off Oman. The studied sedimentary sequence off Oman can be subdivided into three intervals which are characterized by different environmental settings. In the oldest interval (upper Pliocene - lower Pleistocene) the sediments were deposited within a small marginal basin. Water circulation and erosion of sedimentary matter were restricted by a structural barrier. High productivity of surface waters resulted in the [...]
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